Display screen or portion thereof with a graphical user interface



The sole FIGURE is a display screen or portion thereof with a graphical user interface showing the new design.

Within the drawing, the dotted lines and the areas within the dotted lines show unclaimed portions of the display screen or portion thereof with a graphical user interface, and form no part of the claimed design. The perimeters of the portion of the underlying portion of a display screen and the graphical user interface are understood to be flush. 

CLAIM The ornamental design for a display screen or portion thereof with a graphical user interface, as shown and described. 